The present invention relates to the hydrogenation of esters to alchols using a solid hydrogenation catalyst.
The hydrogenation of esters to alcohols is well known. See, for example, U.S. Pat. No. 1,605,093 disclosing the following ester hydrogenation reaction: EQU R.COO.R' + 2H.sub.2 = R.CH.sub.2 OH + R'.OH
according to the 1,605,093 patent, a copper catalyst is used in the ester hydrogenation.
It is frequently stated that the best method of converting an acid to the corresponding alcohol usually involves proceeding through the ester. Esters are normally obtained from acids in nearly quantitative yields, and the esters can be reduced to alcohols, usually with considerably higher yields than in reducing the corresponding acid to the alcohol. Esters have been reduced using various means such as lithium aluminum hydride, sodium plus an alcohol, or a solid hydrogenation catalyst. These methods are indicated in general by the equations below: ##STR1##
Besides copper chromite as an ester hydrogenation catalyst, as indicated in the last equation above, other hydrogenation catalysts, such as the copper chromite/barium catalyst in U.S. Pat. No. 2,091,800 to Homer Adkins et al, have been disclosed.
U.S. Pat. No. 2,093,159 discloses a
"process for the catalytic hydrogenation of esters of aliphatic alkylmonocarboxylic acids, which comprises passing the said esters together with hydrogen while heating to a temperature of the range from 200.degree. to 400.degree. C. over a hydrogenating catalyst essentially comprising cobalt in combination with an activating substance, selected from the class consisting of oxides of metals giving acids with oxygen and compounds of alkali, alkaline earth and rare earth metals with metal acids until substantial quantities of alcohols corresponding to the said alkylmonocarboxylic acid radicles are formed." PA1 "Suitable catalytic substances are for example copper, nickel, silver, zinc, cadmium, lead or cobalt or mixtures thereof and they may be prepared from their salts, oxides or other compounds prior to or after an incorporation with activating substances. The activating substances may be chosen from compounds of the metals giving acids with oxygen, such as chromium, molybdenum, tungsten, uranium, manganese, vanadium or titanium or mixtures thereof as well as from compounds of the alkali, alkali earth or rare earth metals." PA1 ". . . if the hydrogenation of a fatty glyceride is to be operated for the production of alcohols and esters to the substantial exclusion of hydrocarbons it is preferable to select as the catalyst a composition comprising a member of the group of nonferrous hydrogenating metals such as copper, tin, silver, cadmium, zinc, lead, their oxides and chromites, and oxides of manganese and magnesium. Especially good results are obtained with finely divided copper oxide, either wholly or partially reduced and preferably supported upon an inert surface-extending material such as kieselguhr, or promoted by such oxide promoters as manganese oxide, zinc oxide, magnesium oxide, or chromium oxide. The above mentioned mild-acting catalysts may be termed the alcohol-forming catalysts to distinguish them from the more energetic ferrous metal groups. Elementary nickel, cobalt, and iron when suitably supported on kieselguhr may be used to effect the reduction of fatty glycerides with hydrogen, but in these cases the product contains besides alcohols and waxes a preponderance of hydrocarbons, and this disadvantage in most cases will prove so serious as to preclude the use of these catalysts unless the hydrocarbons themselves are the desired end products." Other patents which disclose catalysts for hydrogenation of esters and carboxylic acids include U.S. Pat. Nos. 2,110,843; 2,118,007; 2,121,367; 2,782,243; 3,173,959 (copper-zinc chromite catalyst for ester reduction); 3,267,157 (activated copper chromite catalyst for acid and ester hydrogenation). PA1 "In place of magnesium oxide, other metal oxides which promote the activity of the copper oxide may be employed such, for example, as an oxide of nickel, iron, cobalt, manganese, chromium, calcium, barium, strontium, potassium, caesium, zinc, cadmium and silver, or mixtures thereof." PA1 "The catalyst is inactivated if, through excessive temperatures in the preparation or use of the catalyst, the cupric oxide reacts with cupric chromite to give cuprous chromite, Cu.sub.2 Cr.sub.2 O.sub.4, and oxygen. However, the most frequent cause of inactivation of the catalyst is the reduction of the cupric oxide to copper. This is evidenced by a change in the color of the catalyst from black to a copper red. Such a deactivation of the catalyst is favored by the presence of water, acids, or ammonia in the reaction mixture. The reduction and inactivation of the catalyst may be minimized by precipitating barium (or strontium or calcium) chromate along with the basic copper ammonium chromate in the first step in the preparation of the catalyst."
According to the disclosure of U.S. Pat. No. 2,093,159,
U.S. Pat. No. 2,109,844 teaches away from the use of cobalt-containing catalysts in converting esters to alcohols. At page 5 the 2,109,844 patent states:
U.S. Pat. No. 2,285,448 discloses hydrogenation of glycolic acid and its esters to obtain ethylene glycol. According to the 2,285,448 patent, a copper-magnesium catalyst is preferred. At column 2, line 46 of the 2,285,448 patent it is stated that: